Seal on sacks



Oct. 21, 19.69 E. F. wxEHAHN 3,473,725

SEAL 0N SAGKS Filed March 25, 1968 .ERHL PRANQS WlEHAHNInvenior BMLMMRL i2 Altorney$- 3,473,725 SEAL N SACKS Eric Francis Wiehahn, Vanderbijl Park, Transvaal, Republic of South Africa, assignor to Fisons (Proprietary) Limited, Johannesburg, Transvaal, Republic of South Africa Filed Mar. 25, 1968, Ser. No. 715,846 Claims priority, application Republic of South Africa, Mar. 30, 1967, 67/ 1,837 Int. Cl. B65d 33/16 lU.S. Cl. 229-62 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a seal on plastic sacks and bags, which is adapted to permit occluded or liberated gases or vapours to escape, and to prevent moisture from enteringr from outside, which comprises a longitudinally folded capping strip positioned over the open end of the sack or bag, with sealing lines sealing the capping strip to the walls of the sack or bag, and a further sealing line sealing the walls of the sack or bag together with an interruption at at least one point.

The interruption is created by providing a suitable barrier material between the walls of the sack or bag at the desired point during the sealing operation. A suitable barrier material is, for example, printing ink. Alternatively, a suitable barrier material, e.g. the same material as that of the sack and the capping strip, may be positioned between the walls of the sack or bag and the capping strip at the desired point, to prevent heat penetration sufficient to seal the walls of the sack together.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a seal provided on sacks and bags, preferably thermoplastic plastic sacks and bags, which is adapted to permit occluded or liberated gases or vapours to escape, and at the same time to prevent or at least hinder moisture to enter the sacks and bags from outside. The invention concerns also a method of providing such a seal.

SUMMARY OF THE INVENTION According to the invention, an open end of a tube suitable for the formation of a sack or bag is provided with a seal which comprises a capping strip folded along a fold line to present two flaps, the capping strip being positioned over the two walls of the open end of the tube forming the sack or bag with one ap on either side of the sack or bag; an internal sealing line extendingalong the length of the capping strip and spaced from the fold line and sealing the two walls of the tube forming the sack or bag together, and two external sealing lines sealing the walls to the two flaps of the capping strip; the internal sealing line being interrupted at at least one point along its length in that the two lwalls of the tube forming the sack or bag are not sealed together at that point.

Occluded or liberated gases and vapours inside the sack or bag can escape from the sack or bag between the walls of the sack or bag at the point of interruption of the seal, and by moving transversely along the channel space between the fold line of the capping strip and the internal sealing line to escape at the free ends of the capping strip. The caliper of the sack or bag wall and the dimensions of the interrupted portion will, inter alia, determine the pressure at which occluded or liberated gases and vapours will escape.

The tube forming the sack or bag is preferably a tube of a thermoplastic synthetic plastic material.

nited States Patent O "ice lf desired, one or both of the external sealing lines may also be interrupted at one or more points along their length, to permit the gases or vapours to escape.

A seal according to the invention may be provided for the closure of one or both ends of a sack or bag.

The internal sealing line should extend along the entire width of the open end closed thereby, with the exception of the interrupted portion or portions.

The capping strip may consist of any suitable material. Preferably it consists of a heat sealable material, such as a suitable synthetic thermoplastic material. The sealing lines may then be lines of heat sealing, which may be brought about by any suitable heat sealing apparatus, such as a rotary type sealing apparatus.

In practice, the spacing between the internal sealing lines and the fold line of the capping strip should be relatively small. In fact, if the spacing is too large, it is not impossible that moisture may enter the channel space defined and eventually the sack or bag. Therefore, it is preferred that the spacing be small, or the order of 1A; inch. The spacing must only be large enough to permit gas and vapour to escape that way.

According to the invention, the interruptions in the internal sealing line may be of such dimensions as to permit gas or vapour to escape at a desired pressure. It has been found that interruptions of a length of the order of 0.3-0.8 inch give favourable results in practice. Preferable the interruptions may have a length of about 0.5 inch. It should be understood that the larger the interruptions, the lower the pressure will be at which gases or vapours will escape.

Although a sack or bag may be provided with an internal sealing line having a single interruption, it is preferred to provide two spaced interruptions, one in the proximity of either end of the internal sealing line. For example, in a bag having a width of about 21 inches, the interruptions may be provided about 3 inches from either side. This arrangement has specific practical advantages, particularly that the sack will not seriously be weakened along the sealing line by the interruptions, if the latter are located in the proximity of the ends of the internal sealing line where the forces of strain or impact acting upon the seal are relatively small.

According to a further feature of the invention, those areas of the sack or bag walls facing each other at a point of interruption, may be coated with a substance which has no adherence to itself, so that the walls will open relatively easily to permit gases or vapours to escape. It has been found that the substance with which the wall areas may be coated, may conveniently be printing ink of the type which is normally used for printing on synthetic plastic material, such as polyethylene or polyvinylchloride. For example, the printing ink commercially available under the trade name Coates Briteflex Flexo gives favourable results in practice. A

Alternatively, the areas may be coated with a substance having a certain degree of adherence to itself or tackiness, so that the walls will adhere to one another and will open only when the pressure inside the sack 0r bag reaches a predetermined value.

The invention extends also to a method of producing a seal according to the invention, which method comprises the steps of positioning a longitudinally folded capping strip over the open end of a tube suitable for forming a sack or bag so that a ap of the capping strip is positioned at either side of the sack or bag, sealing the walls of the tube forming the sack or bag and the capping strip together respectively along an internal sealing line sealing the two walls of the sack or bag together, and two external sealing lines sealing the walls to the two flaps, the sealing lines extending along the open end, and interrupting the internal sealing line at one or more points by not permitting sealing of the walls of the tube forming the sack or bag to one another at that point or those points.

The capping strip may, as already indicated, advantageously be a strip of heat scalable material, e.g. of suitable synthetic thermoplastic material, so that the sealing may be brought about by heat sealing.

The internal sealing line may conveniently be interrupted by positioning a barrier material between the walls of the sack or bag, or between the walls and the aps of the capping strip, at the point where the interruption is required, the barrier material being adapted to prevent the interfaces of the walls of the sack or bag from being sealed together. The barrier material may be positioned between the walls of the sack or bag, and then the barrier material should be incompatible with the material of the sack or bag, even at elevated temperatures, and should be adapted to remain in position during the sealing process. The term incompatible when used in this context should be interpreted to mean that the barrier material will not fuse with the material of the sack or bag on the normal contact surfaces, under sealing conditions. In one embodiment, the barrier material may comprise a finely divided solid phase stabilised in a liquid carrier phase.

In practice, it has been found that certain types of printing ink can be used as the barrier material with favourable results, such as printing ink of the type normally used for printing on synthetic plastic material. For example, the ink which is commercially available under the trade name Coates Briteex Flexo has been been ifound to give favourable results in practice. Nail varnish or certain paints may also be used as a barrier material. Alternatively, the barrier material may also be a strip of incompatible material, such as aluminium foil, pressure sensitive cellulose adhesive tape, and the like.

In an alternative way, the barrier material may be positioned between the walls of the sack or bag and the aps of the capping strip, and may then be adapted to serve as an insulating material to prevent the heat sealing of the interfaces of the sack or bag. In this case, the barrier material may comprise a compatible synthetic plastic material. The term compatible when used in this context, should be interpreted to mean a material which Will adhere to or fuse with the material of the sack or bag and the capping strip under sealing conditions. Thus, a compatible material would for example be the same synthetic plastic material as the material of the sack or bag and the capping strip.

In one embodiment, the compatible synthetic plastic material may be applied to the walls of the sack or bag in molten state and is permitted to solidify on the walls. The plastic material may thus be a so-called hot-melt material.

The thickness of the barrier material provided between the walls of the sack or bag and the flaps of the capping strip, should be suicient to prevent the heat from reaching the interfaces of the walls of the sack or bag to seal them together.

As indicated above, the interruptions may have a length of the order of 0.3-0.8 inch. Furthermore, two spaced interruptions may be provided, one in the proximity of either end of the internal sealing line. The interruptions may be provided at those points where the forces of strain or impact acting upon the internal sealing line, are relatively small.

It should be understood that the interruptions in the internal sealing line may be brought about in any other suitable manner.

BRIEF DESCRIPTION OF THE DRAWING The invention and the manner in which it may be carried out in practice will now be described by way of example, with reference to the accompanying drawings.

In the drawings,

FIGURE 1 is a diagrammatic representation of the open end of a plastic sack;

FIGURE 2 is a diagrammatic front View of the sack. embodying the seal according to the invention;

FIGURES 3 and 4 are diagrammatic cross-sectional views of part of the sack and capping strip, taken along line A-A in FIGURE 2, but prior to sealing and illustrating two different applications of a barrier material;

FIGURE 5 is a diagrammatic cross-sectional view or part of the sack and capping strip corresponding to FIGURES 3 and 4, but after sealing;

FIGURES 6 and 7 are diagrammatic vertical sections of part of the sack and capping strip, taken along line B--B in FIGURE 2, but prior to sealing and illustrating two different applications of a barrier material in the same manner as in FIGURES 3 and 4; and

FIGURE 8 is a diagrammatic vertical section of part of the sack and capping strip corresponding to FIGURES 6 and 7, but after sealing.

The drawings illustrate diagrammatically and by wav of example, two ways in which a seal according to the invention may be provided at the open end of a plastic sack.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, the walls 12, 14 of the open end of a sack generally indicated as 10 are provided with strips 16 of a barrier material. The barrier material is applied between the interfaces of the walls l2, 14 and is incompatible printing ink of the type normally used for printing on synthetic plastic material, e.g. the printing ink commercially available under the trade name Coates Briteex Flexo, in the embodiments illustrated in FIGURES 3 and 6. It will be appreciated that the barrier material need -be applied only on one wall 14. In the embodiments illustrated in FIGURES 4 and 7, the barrier material is applied to the external faces of the walls 12, 14 and is a compatible hot-melt synthetic plastic material. In this case, the barrier material should be applied to the external faces of both walls 12, i4. The strips 16 are about 0.3-0.8 inch in width, preferably about 0.5 inch, and are located towards the sides of the sack 10.

A longitudinally folded capping strip 18, presenting a fold line 19 and aps 18a, 18b is positioned over the walls 12, 14. An internal sealing line as shown at 20. and external sealing lines as shown at 23 are provided respectively between the walls 12, 14 and along the capping strip 18 by heat sealing. The sealing lines 20, 23 are spaced from the fold line 19 of the capping strip 18, to dene a channel space 22.

The barrier material strips 16 prevent the walls l2. 14 to be sealed together at those points, and thus provide two interruptions 17 in the sealing line 20. The interruptions 17 occur in the following manner: In the embodiment shown in FIGURES 3 and 6, the barrier material is incompatible with the material of the sack, and due to its physical presence prevents the walls i2, 14 to be sealed together at these points. In the embodiment shown in FIGURES 4 and 7, the barrier material is compatible with the material of the sack and the capping strip and thus permits the walls 12, 14 to be sealed to the capping strip iiaps 18a, 1813. However, it takes up so much of the heat of sealing, that it serves as an insulating material to prevent enough heat from reaching the interfaces of the walls 12, 14 to seal them together.

Occluded gases or vapors in the sack 10 are permitted to escape by passing out through the interruptions 17. and by moving transversely along the channel space 22 to escape at the free ends 24, 26 of the capping strip 18. Due to the small dimensions of the channel space 22 and the interruptions 17, and due to the length et the channel space 22, moisture is prevented or at least hindered to enter into the sack 10.

I claim:

l. A bag formed of a seamless tube of a heat sealable synthetic plastic material, at least one open end of which is provided with a seal which comprises a capping strip of a heat sealable material folded along a fold line to present two flaps, the capping strip being positioned over the two walls of the open end of the bag with one ap on either side of the bag; an internal heat sealing line extending along the length of the capping strip and closely spaced from the fold line and sealing the two walls of the bag together, and two external heat sealing lines sealing the walls to the two flaps of the capping strip; the internal sealing line being interrupted at at least one point in that the two walls of the bag are not sealed together at that point, the point being in the proximity of an end of the internal sealing line and so located that the forces of strain or impact acting upon the internal sealing line will be relatively small, and the interruption being provided by coating the inside face of at least one wall of the bag at the said point prior to heat sealing with a barrier material adapted to prevent the interfaces of the Walls from being sealed together at that point.

2. A plastic bag according to claim 1, in which those areas of the bag walls facing each other at a point of interruption, are coated with a tacky substance having a certain degree of adherence to itself, so that the walls will adhere to one another and will open only when the pressure inside the bag reaches a predetermined value.

3. A method of producing a seal across the open end of a seamless tube of a heat scalable synthetic plastic material to form a bag, which comprises the steps of positioning a longitudinally folded capping strip of a heat sealable material over the open end of the tube forming the bag, so that a flap of the capping strip is positioned at either side of the bag, heat sealing the walls of the tube forming the bag and the capping strip together respectively along an internal sealing line sealing the walls of the bag together and two external sealing lines sealing the walls to the two flaps, the sealing lines extending along the open end and the internal sealing line being closely spaced from the fold line of the capping strip, and interrupting the internal sealing line at at least one point by coating the inside face of at least one wall of the tube at the said point prior to heat sealing with a barrier material adapted to prevent sealing of the interfaces of the walls of the tube forming the bag to one another at that point, the point being in the proximity of an end of the internal sealing line and so located that the forces of strain or impact acting upon the internal sealing line will be relatively small.

4. A method of producing a seal across the open end of a tube of a heat seala'ble synthetic plastic material to form a bag, which comprises the steps of positioning a longitudinally folded capping strip of a heat sealable material over the open end of the tube forming the bag, so that a flap of the capping strip is positioned at either side of the bag, heat sealing the walls of the tube forming the bag and the capping strip together respectively along an internal sealing line sealing the walls of the bag together and two external sealing lines sealing the walls to the two aps, the sealing lines extending along the open end, an interrupting the internal sealing line at at least one point by positioning a barrier material between the walls of the bag and the aps of the capping strip at the point where the interruption is required, the barrier material being adapted to prevent sealing of the interfaces of the walls of the tube forming the bag to one another at that point.

5. A method according to claim 4, in which the barrier material is adapted to serve as an insulating material to prevent the heat from sealing the walls of the bag together, during the heat sealing.

6. A method according to claim 5, in which the barrier material comprises a compatible synthetic plastics material.

7. A method according to claim 6, in which the compatible synthetic plastics material is applied to the walls of the bag in molten state and is permitted to solidify on the walls.

References Cited UNITED STATES PATENTS 3,141,601 7/1964 Ayres et al. 229-62 3,237,844 3/1966 Hughes 229--62-5 3,394,871 7/1968 Williams et al. 229-62-5 DAVID M. BOCKENEK, Primary Examiner U.S. Cl. X.R. 

